You cant split the current between two contactors because in a 240V single phase center tap application the current flows between the two hot legs of the circuit
The link you posted said the contactor is good for 28A at 240V, so youll blow the contactor when using a 50a load.
If you want a cheap 2phase 50A resistive contactor you can get them HERE
for ~$11 each plush shipping
once you get the correct contactors, you wire them up like the picture attached, although if your having trouble understanding the contactors you might want to reassess what your attempting, tell us everything you want to do, and we can all help to make sure your set up is safe